It's just 3 p.m. in Las Vegas when the door to the Mayweather Boxing Club swings open and the show begins. For most fighters, media day is a chore, a duty forced on them by promoters and publicists. For Floyd Mayweather Jr., it's oxygen. Within seconds of his arrival, reporters envelop boxing's biggest star in a sea of microphones and notebooks, and for 30 minutes Mayweather fields questions—about his fight with Victor Ortiz this Saturday night, to be shown on HBO pay-per-view, about a future fight with Manny Pacquiao, about his rocky relationship with his father. He answers every one. He smiles during most.

As great as Mayweather is in the ring (a 41--0 record and six titles in five weight classes), he is equally skilled out of it. He has a politician's knack with the media—never getting rattled, never veering from the narrative. Ask Mayweather about Pacquiao, and he will find a way to praise his own advisers Al Haymon and Leonard Ellerbe and declare with conviction that "all roads lead to Floyd Mayweather." Ask him about Guantanamo Bay, and chances are he will do the same.

Whenever the cameras are on, so is Mayweather. A public workout is a performance, the ring a stage. "Turn the air off," Mayweather barks at a member of his team. "You can't cook with cold grease." The gym heats up, and so does Mayweather. "Oh, I'm so great," he croons as his gloves slap against the pads held by his uncle and longtime trainer Roger Mayweather. "Oh, I'm so good. They can't believe no fighter can beat me." This is Money Mayweather, unplugged. It's a cocky, villainous character Mayweather has created and one that has lifted him from a niche fan base into the mainstream. Mayweather is the biggest PPV draw in boxing history, generating 6.9 million buys over seven fights that have raked in $375 million in revenue. His success on HBO's 24/7—the four most-watched episodes in the series' four-year history involved Mayweather—helped him land a spot on Dancing with the Stars and a sponsorship deal with AT&T.

But, his team stresses repeatedly, it is just a character. "This is the entertainment business," says Ellerbe, "and Floyd is the ultimate entertainer." Money Mayweather is a foul-mouthed bad boy who sets fire to $100 bills in nightclubs. Floyd Mayweather is a family man who donates hundreds of thousands of dollars to charity. Money Mayweather spouts racist, homophobic rants about Pacquiao on the Internet. Floyd Mayweather paid for the funerals of former super featherweight champion Genaro Hernandez and his own longtime photographer, Henry Booth.

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Lately, though, the line between the person and the character has blurred. Mayweather's relationship with his father is fractured, possibly beyond repair. He is a defendant in six civil and criminal cases, the most serious of which—a multiple felony case stemming from a domestic violence incident last September—carries a maximum penalty of 34 years in prison. His relentless bashing of Pacquiao could cost him tens of millions in a defamation suit. As Mayweather prepares for his first fight in the ring in 17 months, his battles outside it are multiplying.

BOTH MAYWEATHER and his father, Floyd Sr., have galactic egos, which is why it's often difficult for them to be in the same room. That was the case last month, when a seemingly good-natured debate about two female fighters escalated into an ugly scene. Junior called Dad a "cab driver" as a fighter and a "bum-ass trainer," who was dumped by Oscar De La Hoya. Floyd Sr. said he built Junior and that his son would be 41--1 if the two ever came to blows. Every word was captured by HBO. The video has since gone viral.

Jeff Mayweather, brother to Floyd Sr. and Roger and a former IBO super featherweight champion, saw this coming. In 1999 he was among the onlookers who had to separate Floyd Sr. from Floyd Jr. after a disagreement during training nearly turned violent. Jeff helped defuse the situation by asking Junior how he would feel if he kicked his father out of camp and Senior, a convicted drug dealer, went back to his old line of work. It was a temporary truce; Floyd fired his father and evicted him from his home a year later. "That fight was building for a while," says Jeff. "It's tough for Floyd Sr. to see his son be so successful when he is not with him. And when little Floyd hears his father talking about himself so much, it irritates him."

Irritates, but not distracts. Mayweather seems to have an uncanny ability to compartmentalize, to shut out the outside world and lock in on the task at hand. "When someone has been doing something all their life, it's easy to block things out," says Roger. "His only goal is winning. He doesn't focus on what people say or what people think. He just focuses on what he needs to do to win."

For his part, Mayweather genuinely appears impervious to outside influences. Ask him about his father, and he says that he doesn't care if he ever sees him again. Ask him about the alleged incidents with Josie Harris, the mother of three of his children, who has accused Mayweather of beating her and threatening the kids (a preliminary hearing is set for Oct. 20), and Mayweather calls them "lies" and says "show me the pictures." Ask him about Pacquiao's lawsuit, and Mayweather—who has claimed Pacquiao was on "power pellets"—denies ever directly accusing Pacquiao of using performance-enhancing drugs. "If you're scared to take the test," says Mayweather, "obviously you are hiding something."

There is something that could rattle Mayweather, though: losing. He sees his perfect record as uncontestable proof of his greatness. His logic, of course, is flawed. Sven Ottke (34--0) retired undefeated, but no one will argue that Ottke is better than Sugar Ray Robinson (19 losses) or Muhammad Ali (five). "Robinson fought 23 world champions," says boxing historian Bert Sugar. "Mayweather doesn't have the same credentials."

Still, Mayweather believes his own hype. More important, he uses it to control his world. He turned down interviews with magazines (including SI) because they would not promise him a cover. He declares himself the greatest, which sparks a media debate, which keeps him relevant. Mayweather needs to be relevant. His vitriolic rant at Pacquiao was posted during Pacquiao's press tour for his fight with Antonio Margarito. When the media jumped on Ortiz's tragic backstory, Mayweather called it boring and said black athletes go through such struggles all the time. When De La Hoya revealed his battles with substance abuse, Mayweather tweeted that De La Hoya was a "drug user, dresses like a drag, committed adultery and drinks alcohol and Ortiz looks up to this guy."

Words from the man or from Money? At this point, who knows? If Mayweather beats Ortiz on Saturday night at the MGM Grand in Las Vegas, the character will live on, free to tout his superiority, flaunt his wealth and hold hostage a world awaiting a showdown with Pacquiao. Lose, and a $50 million payday from a Pacquiao bout will be flushed and a big part of the character along with it. Money Mayweather, the undefeated king, will be no more. Of everything at stake for Mayweather on Saturday, nothing matters more.

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For previews and analysis of Mayweather-Ortiz, go to SI.com/boxing and HBO.com/boxing

MAYWEATHER SEES HIS PERFECT RECORD AS PROOF OF HIS GREATNESS. HE BELIEVES HIS OWN HYPE AND USES IT TO CONTROL HIS WORLD.

PHOTOPhotograph by SCOTT HEAVEY/GETTY IMAGES

COMFORT ZONE Famous for his freakish ability to compartmentalize, Mayweather, boxing's biggest draw, is most at peace in the gym, where he can turn a public workout session into performance art.